72 UNITED STATES NATIONAL MUSEUM BULLETIN 251 



Colonies pale grayish brown, although many calcareous spicules pres- 

 ent in test. Spicules very large, 77-llOjLt in diameter, 87/x on an aver- 

 age, somewhat transparent, confined to only the surface and bottom 

 layers, leaving the layer containing zooids quite free from spicules. 

 Rays of spicules short, acutely pointed at tip, rather numerous, from 

 13 to 19 on the equatorial plane. Zooidal layer reddish brown, possibly 

 stained by dark pigments of Polycarpa cryptocarpa (Sluiter) which 

 was preserved in the same bottle with the present specimens ; somewhat 

 fibrous in consistency and very tough. All thoraces so strongly con- 

 tracted that it is quite impossible to measure the length accurately. 

 Atrial aperture a wide opening; 4 rows of stigmata present, about 6 

 stigmata in each row. Abdomens very small (290;^ in an examined 

 specimen) and embedded in the spiculeless zooidal layer. No gonads 

 found in any zooids examined. 



Eemarks. — The extraordinary size of spicules is characteristic of the 

 present new species. As the thoraces are strongly contracted and the 

 abdomens are devoid of any well-defined gonad, it is impossible to 

 clarify the subgeneric situation of this new species, although it prob- 

 ably belongs to the subgenus Didemnum as is seen in figure 22c?. 



24. Didemnum. (Didemnum) siphonale, new species 



Figure 23 



HoLOTYPE. — USNM 11804; Japan: Honshu Island, off Manazuru 

 Zaki N.8°W., 4.5 miles, 153 fathoms, green mud, volcanic ash and 

 sand ; Albatross sta. 3698, May 5, 1900. 



Paratypes. — USNM 11805 : same data, 7 specimens. 



Description. — Eight colonies are in the material ; tlie largest (holo- 

 type) is 15 mm. X 10 mm. in extent and 1.5-2 mm. in thickness. They 

 are all whitish in color and encrusting the surface of a specimen of 

 Herdinania Tnomus (Savigny). Usually a single large and oval com- 

 mon cloacal aperture, up to 1 mm. in long diameter, is found near the 

 center of respective colonies; it is always opened at the tip of a short 

 siphon, the inner surface of which is folded as shown in figure 23a. 

 The whole colony surface shows a kind of cerebral appearance, for 

 it is divided into a number of low elevations each covering one to 

 three zooids. In the grooves between these elevations are found 

 sparsely scattered minute prominences formed by the aggregation of 

 calcareous spicules; they may grow up to small finger-shaped pro- 

 tuberances in some colonies (fig. 23^) or may be quite absent in some 

 others. Spicules small, distributed densely and evenly throughout 

 test from bottom to surface; superficial spiculeless layer extremely 

 thin. Spicules are only 12-18;a in diameter, 14/i, on an average; rays 

 short, bluntly tipped and 7-9 on the equatorial plane. Lacunae sys- 

 tem very spacious, extending not only in thoracic layer but also to 



